1. Field of the Invention
The present invention relates to a pattern analyzer for analyzing a pattern of a seal or stamp on a bill, check or the like in a binary representation, and for detecting whether or not the bill in question is true or counterfeit, by way of a comparison of the analyzed result of a seal of the bill in question with stored data indicating the analyzed result of a true seal previously obtained.
2. Description of the Prior Art
It is known in the art to analyze a pattern by the steps of reading the pattern by a reading device, obtaining shade signals indicating the depth of shade of color at sampling points, and converting the shade signal at each sampling point to an analyze signal in binary form representing either black or white.
To discriminate automatically whether or not a pressure marked seal or stamp on a bill is genuine or counterfeit, the prior art method follows the steps of obtaining analyze signals of the stamp in question at sampling points through the above-mentioned steps, and comparing analyze signals with previously memorized signals representing the analyzed result of the genuine stamp mark.
According to one example of the prior art, the shade signal at each sampling point is converted to an analyze signal in such a manner that the shade signal is compared with a predetermined fixed threshold level to divide the shade signal typically between two types of signals, for example, "1" representing black, and "0" representing white. In this case, the analyze signal is a 1-bit binary signal. Thus, an image of the stamp mark is recognized by means of a plurality of 1-bit analyze signals, such as in a newspaper picture drawn with only black and white dots.
When stamping a mark on bills with an application of pressure, the stamped marks on the bills may have different brightness distributions in repeated stampings, due to the differences in various factors, such as stamping pressure, stamping angle, hardness of the base on which the bill is placed, and the type and amount of ink applied to the stamp face. Furthermore, a change in the amount of illumination directed to the stamped mark will also cause a different brightness distribution. Such differences result in different shade signals.
Since the threshold level is fixed, the analyze signals according to the prior art may result in inconsistencies, for example that one stamp mark has a wide area occupied with "1s", whereas another stamp mark has a small area occupied with "1s", although the stamp used is the same. Furthermore, such an inconsistency may also occur when stamp marks are placed on bills of different colors.
Thus, the pattern analyzer according to the prior art is not suitable for discrimination between genuine and counterfeit stamp marks.